Nonwoven elastic fabrics have been the subject of considerable attention and effort. Elastic fabrics are desirable for use in bandaging materials, garments, diapers, supportive clothing and personal hygiene products because of their ability to conform to irregular shapes and to allow more freedom of body movement than fabrics with limited extensibility.
Elastomeric materials have been incorporated into various fabric structures to provide stretchable fabrics. In many instances, such as where the fabrics are made by knitting or weaving, there can be a relatively high cost associated with the fabric. In cases where the fabrics are made using nonwoven technologies, the fabric can suffer from insufficient strength and only limited stretch and recovery properties.
Elastomers used to fabricate elastic fabrics often have an undesirable rubbery feel. This is particularly true with thermoplastic elastomers rather than cross-linked elastomers. When these materials are used in composite nonwoven fabrics, the hand and texture of the fabric can be perceived by the user as sticky or rubbery and therefore undesirable.
Nonwoven fabrics having thermoplastic elastomers incorporated into the fabric structure can be extremely difficult to process and to manufacture. For example, tension control during fabric manufacture and/or during downstream processing can be extremely critical. A small change in tension can result in stretching or recovery of the fabric which can lead to a non-uniformly manufactured product. Tension control is even more aggravated when heating is required, for example, during fabric drying, adhesive application, lamination, thermal bonding or other thermal treatment. When subjected to heat and tension, the fabric can stretch and otherwise distort more readily than when the fabric is at room temperature. In addition, thermoplastic elastomers can lose elastic properties when stressed at elevated temperatures and allowed to cool partially or fully while under such stress, and/or the thermoplastic fibers and filaments are apt to break, thereby causing the elastic fabric to lose a portion or all of its elastic properties. Still further, when elastic fabrics are wound into rolls, stretching of the fabrics can occur during the winding process and the fabric can lose elastic properties during its subsequent storage due to the phenomenon of creep.
Yet another difficulty encountered when processing and manufacturing nonwoven fabrics having thermoplastic elastomers incorporated therein is coverage ability. When elastic fabrics are stretched, the webs are reduced in thickness, and exhibit a corresponding decrease in coverage ability, i.e., exhibit voids or thin areas in the fabric.
U.S. Pat. No. 4,775,579 to Hagy, et al. discloses desirable composite elastic nonwoven fabrics containing staple textile fibers intimately hydroentangled with an elastic web or elastic net. One or more webs of staple textile fibers and/or wood pulp fibers can be hydroentangled with an elastic net according to the disclosure of this invention. The resulting composite fabric exhibits characteristics comparable to those of knit textile cloth and possesses superior softness and extensibility properties. The rubbery feel traditionally associated with elastomeric materials can be minimized or eliminated in these fabrics.
U.S. Pat. No. 4,413,623 to Pieniak discloses a laminated structure such as a disposable diaper which can incorporate an elastic net into portions of the structure. The elastic net can be inserted in a stretch position between first and second layers of the structure and bonded to the layers while in the stretch condition. Subsequent relaxation of the elastic net can result in gathering of the structure.
U.S. Pat. No. 4,525,407 to Ness discloses elastic fabrics which include an elastic member which may be an elastic net intermittently bonded to a substrate which prior to stretching is less easily extensible than the elastic member. The non-elastic member is bonded to the elastic member and the entire composite is rendered elastic by stretching and relaxation.
U.S. Pat. No. 4,606,964 to Wideman discloses a bulk composite web which can be prepared by bonding a gatherable web to a differentially stretched elastic net. Subsequent relaxation of the differentially stretch net is said to result in gathering of the fabric.
The various problems associated with thermoplastic elastomeric materials, as discussed previously, render many of these and other composite elastic fabrics difficult to manufacture and process. There are problems with tension control, elongation under the tension induced by converting machines, irregular cut length, poor tracking, blocking, coverage ability and similar problems. In the past, these problems have been overcome or minimized only with substantial difficulty. To minimize the problem of machine direction stretching during fabric converting and/or forming, for example, typical approaches have been to either cool the thermoplastic elastomer to a temperature below its glass transition temperature or to make "heat activated" materials that are rigid, but then shrink and become elastomeric when heated. These steps are often required to process the material under acceptable tension levels even at ambient temperatures. Alternative process modifications have required extremely exact tension control mechanisms. These, however, do not consistently eliminate problems during normal fabric processing.